Node.js MongooseJS-子文档的填充路径

我在下面的模式中遇到了实际的人口问题。它可能不是最好的模型设计（相对于平均堆栈来说相对较新），但我可以让它填充除规范模型之外的所有内容

// Spec Model
var SpecSchema = new Schema({
  time: { 
    type: Date,
    default: Date.now
  },
  active: {
    type: Boolean,
    default: 'true'
  },
  name: String,
  desc: String
});
module.exports = mongoose.model('Spec', SpecSchema);

// Thing model
var specsSchema = new Schema({
  time: { 
    type: Date,
    default: Date.now
  },
  spec: { 
    type: Schema.Types.ObjectId, 
    ref: 'Spec' 
  },
  value: String,
});
var ThingSchema = new Schema({
  time: { 
    type: Date,
    default: Date.now
  },
  active: { 
    type: Boolean,
    default: true
  },
  title: String,
  specs: [specsSchema]
});
var Thing = mongoose.model('Thing', ThingSchema);

// Set model
var thingsSchema = new Schema({
  time: { 
    type: Date,
    default: Date.now
  },
  active: {
    type: Boolean,
    default: 'true'
  },
  thing: { 
    type: Schema.Types.ObjectId, 
    ref: 'Thing' 
  }
});
var SetSchema = new Schema({
  user: { 
    type: Schema.Types.ObjectId, 
    ref: 'User' 
  },
  time: { 
    type: Date,
    default: Date.now
  },
  active: {
    type: Boolean,
    default: 'true'
  },
  title: String,
  things: [thingsSchema]
});
var Set = mongoose.model('Set', SetSchema);

标准总体很好，但我一生都无法获得

模型。填充
来工作，从我所看到的所有示例和解决方案中，我不清楚该路径是什么

Set.findById(req.params.id)
  .populate('things.thing')
  .populate('user', '_id name')
  .exec(function (err, set) {
    if(err) { return handleError(res, err); }
    if(!set) { return res.send(404); }
      Thing.populate(set,{
          path:'things.thing.specs.spec',
          select: 'name',
          model: Spec
      }, function(err, set){
        if ( err ) return res.json(400, err);
    });
    return res.json(set);
});

任何指向正确方向的指示都将不胜感激

path:'things.thing.specs.spec',
      select: 'name',
      model: Spec

应该是

path:'things.thing.specs.spec',
      select: 'name',
      model: 'Spec'